DESCRIPTION (taken from the application): The broad long-term objective of this project is to understand the coupled interactions among the smooth muscle thin filament protein components, actin, tropomyosin, caldesmon and myosin that are involved in the cooperative activation and relaxation processes. Specifically we aim to: 1) determine the actin and ADP binding properties of dephosphorylated heavy meromyosin; 2) test the hypothesis that slow ADP release from cycling myosin heads are involved in the "latch state" of smooth muscle; 3 test the hypothesis that caldesmon functions by affecting both the thin filament regulatory state and the proximity of myosin to actin; 4) determine the proximity changes between the components of the thin filament that take place on binding heavy meromyosin. The methods to be used include ATPase activity measurements, kinetics and equilibrium titrations with fluorescence probes on the protein components. FRET and crosslinking techniques will be used for proximity information. Tropomyosin isoforms isolated from smooth muscle and mutated tropomyosins will be used. With the information obtained from these studies, the basic mechanisms of smooth muscle regulation will be better understood so that the several smooth muscle abnormalities can be characterized.